The present invention relates to a resistant starch prepared by isoamylase debranching of low amylose starches to form a completely linear short chain α-glucan composition, and its use.
Starch, a complex carbohydrate, is composed of two types of polysaccharide molecules, amylose, a mostly linear and flexible polymer of D-anhydroglucose units that are linked by alpha-1,4-D-glucosidic bonds, and amylopectin, a branched polymer of linear chains that are linked by alpha-1,6-D-glucosidic bonds. Starch is digested predominantly in the small intestine by the enzyme alpha-amylase.
It is known that certain starch processing operations result in the transformation of starch into starch that is resistant to enzymatic hydrolysis within the small intestine, known simply as resistant starch. Resistant starch resists digestion and absorption in the small intestine, and passes into the large intestine where it is fermented by colonic microflora to short chain fatty acids, particularly butyrate, and gases.
Research literature indicates that this fermentation of resistant starch by colonic bacteria has numerous beneficial effects and thus would be useful for both food and drug applications.
Resistant starch may be used in foods, including medical foods and dietary supplements, to maintain colonic health and mucosal integrity. Resistant starch is known as a prebiotic. Further, as it is not utilized until it reaches the large intestine where it is fermented to short chain fatty acids, resistant starch has a reduced caloric value. The reduction in available or glycemic carbohydrate in the small intestine has been linked to improved blood glucose and insulin control, with associated benefits for weight management. Research also indicates that resistant starches may contribute to maintaining a healthy immune system in humans.
Resistant starch may also be used as a drug. It has been linked to a decreased risk for various colonic diseases, including a decreased incidence of cancer. In addition, resistant starch may reduce the risk of the cluster of metabolic disorders associated with Syndrome X including insulin resistance, hyperglycemia, hyperinsulinemia, dyslipidemia, dysfibrinolysis, diabetes, hypertension and cardiovascular disease. It may also be useful for treating obesity.
Resistant starch (RS) has been classified in the literature into four categories depending on the causes of resistance. RS1 is a physically inaccessible starch due to entrapment of granules within a protein matrix or within a plant cell wall. RS2 is a granular starch that resists digestion by pancreatic alpha-amylase. RS3 is a retrograded, nongranular starch or starch food. RS4 is a resistant starch that has linkages other than alpha-1,4- and alpha-1,6-D-glucosidic bonds.
Various methods have been reported for producing the various types of resistant starch. These include U.S. Pat. No. 5,593,503 which describes a method of making a granular resistant starch; and U.S. Pat. Nos. 5,281,276 and 5,409,542 which describe methods of making resistant starches of the RS3-type, all from high amylose starches. U.S. Pat. No. 5,855,946 describes a method of making a resistant starch of the RS4-type by crosslinking and phosphorylating starch. U.S. Pat. No. 6,043,229 discloses a partially degraded and retrograded resistant starch.
Surprisingly, it has now been discovered that completely linear, short chain alpha-1,4-glucans which are highly crystallized result in a starch which is resistant to amylase digestion.